Only here in the New Testament. A governor ruling in the name of a king: a prefect.
Or Hareth, the father-in-law of Herod Antipas. Hs capital was the rock-city of Petra, the metropolis of Arabia Petraea. Herod's unfaithfulness to his daughter brought on a quarrel, in which Herod's army was defeated, to the great delight of the Jews. The further prosecution of the war by Roman troops was arrested by the death of Tiberius, and it is supposed that Caligula assigned Damascus as a free gift to Aretas.
Kept with a garrison (ἐφρούρει)
Imperfect tense, was maintaining a constant watch. Compare Act 9:24 : They watched the gates day and night.